Both environmental and endogenous processes generate pathologically high levels of ROS, with subsequent damage to lipids, proteins and DNA promoting mutation and cell death. However, low levels of ROS are physiologically important in regulating cell proliferation and gene expression.1,2 Cells must thus prevent the detrimental and promote the beneficial aspects of ROS, which suggests that there are precise regulatory strategies to maintain proper ROS levels. We propose to test the hypothesis that cells manage ROS balance by turning-on and turning-off the translation of ROS detoxification and DNA damage response proteins, using the opposing activities of the RNA methyltransferases ALKBH8 and TRM9L. The underlying mechanism arises from our discovery that enzyme-catalyzed methylation signals by ALKBH8, operating at the level of tRNA modification to anticodons, can translationally up-regulate selenocysteine (Sec)-containing ROS management proteins. These RNA modifications are required for stop-codon recoding - the mechanism of reading internal stop-codons as Sec-codons in mRNAs for Sec-containing glutathione peroxidases (GPXs, antioxidants) and thioredoxin reductases (TrxRs, regulate ribonucleotide reductase activity to promote the DNA damage response). We hypothesize that dueling RNA modifications control stop-codon recoding to promote (ALKBH8) or prevent (TRM9L) the translation of Sec-proteins and thus regulate ROS and DNA damage responses. Further, we hypothesize that part of the process of carcinogenicity involves hijacking of RNA modification systems to turn-off stress responses and promote a pro-mutagenic program of ROS-induced DNA damage and decreased DNA repair. To facilitate our studies, we have developed a modification analysis platform to monitor 33 human tRNA modifications and we have demonstrated that anticodon modifications are significantly regulated in response to ROS stress. Together with our RNA modification analysis platform, we will use biochemical, molecular and computational analyses to test our hypothesis in a robust set of normal, cancer- derived and engineerable lines. Importantly, our studies will define a novel system of translational control of stress response, dissect the mechanism a pro-mutagenic program, and reveal new targets and strategies for cancer treatment and prevention.